As a conventional technique which allows even an unskilled person to simply adjust a tappet clearance in an engine valve, a technique is disclosed in the following patent document in which an adjusting screw is driven until displacement of a rocker arm reaches a stability region, thereafter the adjusting screw is loosened until displacement of the rocker arm can be reduced by a reference value with a magnescale to set an adjusting origin, from which the adjusting screw is loosened by an amount corresponding to a predetermined value so as to set a desired clearance. (Refer to Patent document 1, for example)
Patent document 1: Japanese Patent Application Publication No. 2001-27106